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99 Percent Of The Microbes Inside You Are Unknown To Science

September 19, 2017

Written byAshley Hamer

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You have roughly 69 trillion cells in your body, but only about half of those are human. The rest are bacterial — and, we should mention, that figure doesn't even count the many viruses living within you. And those non-human cells? Scientists accidentally discovered that almost all of them are unknown to science. It's a great big, very tiny world in there.

Microbes: The Final Frontier

Some of the best discoveries in science happen by accident (Post-It Notes, anyone?). This is no exception. Stanford researchers were just looking for a good way to know when a patient's body is about to reject a transplant, something easier than the standard needle biopsy. They took blood samples from transplant recipients, analyzed their microbiome — the collection of bacteria, viruses, and other microscopic organisms that live in the human body — and found that if the blood contained a lot of DNA from the organ donor, the organ was probably about to be rejected. Cool! An easy way to detect organ rejection, no biopsy required.

But hold on. In their analysis, they didn't just look at donor DNA — they looked at everything. And they found that of all the tiny organisms setting up shop in the body, 99 percent of them contained DNA that failed to match anything in a genetic database. Nearly all of the microbiome had never been identified by scientists.

What's New?

With their transplant rejection studies published, Stanford professor Stephen Quake and a large team of researchers got to work characterizing these mystery microbes. Many were close relatives of known microbes, which made them easy to identify. The large majority of the new DNA, for example, belonged to a phylum called proteobacteria, to which E. coli and Salmonella belong.

The new viruses were an especially big win. The largest group of viruses they found were in the torque teno family, which aren't generally associated with disease. Among the torque teno viruses scientists do know, one group infects humans, and another infects animals. But among the torque teno viruses these researchers found, many didn't fit in either group. "We've doubled the number of known viruses in that family through this work," Quake said in a press release.

But why were so many of these microbes unknown until this point? That was no mystery to the researchers. Generally, studies that look at the microbiome are very specific: they look at only the gut, or only the skin, or only one kind of microbe. Because the team used a wider lens in their transplant study, they found a lot of microbes that scientists had never thought to analyze before. Accident or not, knowing more about the grand diversity of the human microbiome can teach us more about the infections that can overtake us. That, in turn, can help experts prevent the next global pandemic.